1. Field of the Invention
The present invention relates to an information signal processing unit for detecting additional information from an information signal to which the additional information is added and processing it.
2. Description of the Related Art
Recently, a reproducing unit for a digital video tape recorder (VTR) and a digital video disc (DVD) and software reproducible using these units are provided in numbers, digitized video signal and aural signal can also be reproduced readily at home, and an image and a sound/voice respectively excellent in the quality of an image and a sound/voice can be reproduced.
Digitized video signal and aural signal or a program are plentifully provided via a recording medium such as the Internet and a compact disc read only memory (CD-ROM) and digitized software provided via the Internet, CD-ROM and others is widely utilized using a personal computer and others.
However, in the meantime, there is a problem that software plentifully provided as described above and composed of digitized video signals and others may be unlimitedly copied. Therefore, if digitized information, for example a video signal is dealt with, direct copy preventing control such as copy prohibition is executed by adding a copy preventing code to a digital video signal as digital data and recording it on a recording medium.
Not only a copy preventing code for prohibiting or allowing copy is added but a code for limiting the generation of copy is added to a digital video signal and more flexible control over copy is also executed.
FIG. 1 is a basic block diagram showing a copy system in case digitized information is dealt and the copy system is provided with functions for sending digital information read by a digital information reading device 110 to a digital information recording device 120, copying information which can be copied, prohibiting the copy of information the copy of which is not allowed and updating the following digital information in case a code for limiting the generation of copy exists in digital information.
Copy control information as additional information is recorded in addition to digital main information in a recording medium 111 installed in the digital information reading device 110. The copy control information is provided with the prohibition or allowance of copy, the limitation of a generation and others as control contents.
The reading section 112 of the digital information reading device 110 generates a digital read information signal D2 composed of digital main information and copy control information added to the digital main information based upon a signal D1 obtained by reading information in the recording medium 111 and sends the above signal to the digital information recording device 120.
The additional information reading section 121 of the digital information recording device 120 detects copy control information CC from the received digital read information signal D2 and sends the detected copy control information CC and the digital read information signal D2 to an additional information changing section 122.
The additional information changing section 122 generates new additional information based upon copy control information CC in case copy control information added to a digital information signal D2 is required to be changed and changes copy control information added to the digital information signal D2 by adding the new additional information to the digital information signal D2.
For example, if copy control information CC is generation limited information of which the copy of only a first generation is allowed, the additional information changing section 122 changes copy control information by generating new copy control information the control contents of which represent the prohibition of copy and adding this new copy control information to the digital information signal D2.
As a result, as described above, a digital information signal D3 to which copy control information changed if necessary is added and copy control information CC are output from the additional information changing section 122 and sent to a writing section 123.
The writing section 123 converts the above digital read information signal D3 to digital information suitable for recording if copy control information CC supplied via the additional information changing section 122 represents the allowance of recording a digital read information signal from the digital information reading device 110 and writes the above converted digital information to a recording medium 124. In the meantime, if copy control information CC from the additional information reading section 121 represents the prohibition of copy, the wiring section 123 does not record the above digital read information signal D3.
Further, if copy control information CC from the additional information reading section 121 represents that the copy of only a first generation is allowed, the digital read information signal D3 to which new copy control information is added by the additional information changing section 122 as described above is converted to digital information suitable for recording and is written to the recording medium 124. In this case, a digital information signal cannot be copied using a copied recording medium 124.
As described above, in the case of so-called digital connection that a main information signal and copy control information as additional information are supplied to the recording device as a digital signal, the recording device can securely execute copy preventing control such as the prohibition of copy using copy control information because copy control information is included in transmitted digital data.
As described above, even if information recorded in a recording medium in which a digital video signal as a main information signal and copy control information as additional information are recorded is read using a digital reading device and copy control information is obtained together with a digital video signal, only a digital video signal which is a main information signal can be converted to an analog signal via a D/A converting circuit to monitor an image for example and can be output to an analog output terminal to which a picture tube of a monitor is normally connected.
As described above, even if digital information is read by a reading device, a copy control signal is not included in an analog signal output to the analog output terminal. Therefore, in the case of analog connection in which analog VTR and others are connected to an analog output terminal, control over copy based upon copy control information is disabled, for example the copy of a main information signal the copy of which is prohibited is enabled and the limitation of a generation of copy is also disabled.
As copy control information is often added in a header and others separately from a digital video signal as a main information signal even in the case of digital connection, copy control based upon copy control information is disabled and illegal copy is enabled by deleting information in a part to which copy control information is added and falsifying copy control information such as replacing with another information.
Further, it is also conceivable that when copy control information is superimposed or added in a frequency band different from the frequency band of these video signal and aural signal even if a video signal and an aural signal respectively as a main information signal are an analog signal or a digital signal, copy control information is deleted by a simple frequency filter and copy control based upon copy control information is disabled.
Therefore, as described above referring to FIG. 1, as the signal strength of additional information such as copy control information added to a main information signal is weak and additional information cannot be regenerated in case it is once deleted even if more flexible copy control is executed by providing a function for changing copy control information as additional information to the recording device, changing additional information added to an information signal in recording an information signal if necessary and utilizing the changed additional information, a case that additional information added to an information signal cannot be sufficiently utilized occurs.
The present invention is made in view of the above problems and the object is to enable adding additional information to an information signal without deteriorating the quality of a read information signal so that falsification and deletion are also disabled in a device used by a general user, detecting additional information added to an information signal if necessary and utilizing the additional information.
An information signal processing unit according to the present invention is characterized in that it is provided with reading means for receiving an information signal on which an additional information signal the spectrum of which is spread is superimposed and reading the above additional information signal from the above information signal, additional information signal generating means for generating a new additional information signal based upon the additional information signal read by the reading means, spreading means for spreading the spectrum of the new additional information signal generated by the additional information signal generating means and superposing means for superposing the new additional information signal the spectrum of which is spread by the spreading means on the above information signal and outputting it.
According to the above unit, the spectrum of a new additional information signal is spread and is superimposed on a digital information signal as a wide-band and low-level signal. If the digital information signal is a video signal, the superimposed additional information signal never deteriorates a reproduced image.
Further, as the new additional information signal is superimposed on the digital information signal at the same time and in the same frequency band, it is difficult to falsify or delete additional information by a frequency filter or the simple replacement of information signals.